Weather and seasonal variations greatly affect the amount of solar radiation available to generate power. Experts in solar energy have long realized that the greatest drawback in the use of solar generated electricity or fuels is that energy consumption is not limited to times when direct solar energy is available. The mismatch between the time of production and time of use implies a need for large scale storage of solar generated energy. Today, there is a great need for a process of storing solar generated energy in a readily available form.
Electrolysis of water, using the electrical energy from photovoltaic cells which can convert solar energy to electrical current, can provide a potentially limitless source of hydrogen fuel. However, the single greatest drawback to hydrogen generated by electrolysis or photoelectrolysis has involved the storage of the hydrogen. The energy contained per unit volume for gaseous hydrogen is very low. A volume of about 312.5 liters (L) is necessary to store 1 kilowatt (kWh) of hydrogen at atmospheric pressure and standard temperature, i.e., about 25.degree. C. Clearly, tremendous storage volumes would be necessary for the large amounts of energy industry will require if there is a major conversion to the use of hydrogen gas as a fuel.
In its liquid form, hydrogen is a more compact source of energy. Sufficient liquid hydrogen to generate 1 kWh of electricity requires a volume of only about 0.36 L. However, the cost of cryogenic equipment necessary to maintain the hydrogen in a liquid state at 20.degree. K. or below, is prohibitively expensive.
Metal hydrides, such as MgH.sub.2, LiH, or CaH.sub.2, are potential storage media. However, metal hydride storage would require the use of valuable metals which are not inexhaustable and which require large amounts of energy to mine and refine. Releasing energy stored in metal hydrides requires a further large input of energy because of the high equilibrium temperatures of the materials.
Methanol has been suggested as a combustible chemical compound but has been rejected, among other reasons, for its difficulty in conversion to electricity directly in fuel cells and its adverse environmental effects on burning.
Thus, a search has continued for a chemical compound that can store and release the electrical current obtained from solar energy in an efficient and environmentally satisfactory manner.